Backwashing-type filters used in removing particles in liquid flow systems generally involve placing a filter in a large reservoir and allowing water to rush through the filter, depositing the particles on one face of the filter. Backwashing consists of a valve-controlled reverse flow, flushing the particles from the filter and carrying them to a drain. Refrigerating systems are one example of a liquid system wherein the liquid exposed to the atmosphere collects dirt, leaves, silt, ash, etc., as is discussed in U.S. Pat. No. 2,875,594. One problem prevalent in backwashing filters is that the surface area through which the liquid passes is usually long and generally tubular in shape and of substantial extent and the solid particles do not build up uniformly. Moreover, the backwashing liquid flow is not uniformly applied to the filter medium and difficulty is encountered in removing the particles.
Attempts have been made to provide a uniform liquid flow against the entire surface area of the filter medium. Hirs U.S. Pat. No. 3,169,109 discloses a tapered displacement member within an elongated cylindrical filter medium of uniform diameter throughout its length to uniformly distribute the water pressure over the entire area of the filter medium during a backwashing operation. A backwashing filter currently being manufactured by Ronnigen-Petter uses a backwash diffuser in the center of the filter medium that has a series of tapered sections that deflect the backwash flow to equalize fluid flow.